Research On Contact-impact Events Between Barrel And Bourrelet Of Medium-large Caliber Howitzers

During the launching process of artillery,contact-impact events exist inevitably between the barrel and bourrelet due to the projectile-barrel clearance,generating great excitation to the barrel.Meanwhile,the movement of the barrel and other parts of the artillery in turn affects the inside movement of the projectile.Obviously,the barrel vibration and projectile movement are coupled,which results in the initial disturbances of the artillery system.This determines the movement state of the projectile out of the muzzle,and has a close relationship with the firing accuracy of the artillery system.Therefore,it is urgent to establish an accurate,high-efficiency contact force model between the barrel and bourrelet with full consideration of the complexity of the barrel inner surface.On the basis of this model,the motion law of the projectile can be described,and the coupling mechanism of the artillery movement can be revealed,which is of great significance to predict the disturbance of the projectile at muzzle and improve the firing accuracy of the artillery system.In view of the problems above,the contents can be summarized as two major parts:the derivation of analytical model describing contact-impact events between barrel and bourrelet,and the combination between finite element simulation and parameter identification.Considering the above two aspects,specific research work can be listed as follows:(1)Introducing some basic theories of contact-impact problems from two aspects:one is related to the contact-impact events of rigid multibody system,the other concerns the contact-impact events using Finite Element Method(FEM),which lay some solid theoretical foundation for the following dynamic characteristics analyses of contact-impact events between barrel and bourrelet.As for rigid multibody system aspect,first of all,the general clearance vector mathematical model of revolute clearance joint is developed and the contact detection strategy is given.Then,the dynamic equation of rigid multibody system with clearance is derived based on the Lagrange equation of the first kind.Combined with the Baumgarte stabilization technique,the responses of the system can be solved using the variable step size fourth-fifth-order Runge-Kutta-Fehlberg(RKF45)numerical integration method.With regard to the FEM numerical simulation of contact-impact problem,the following aspects are introduced,including the constraint condition,the contact detection method,material elastoplastic properties,two kinds of plastic yield criteria and hardening rules.The penalty function method is used to describe the contact-impact process between barrel and bourrelet.Solution strategy of the explicit dynamic equation is also presented.(2)Considering the limitations of the traditional contact force models,a new hybrid analytical contact force model is proposed based on the elastic foundation model and Gaussian quadrature.The hybrid model is applied to the contact-impact process between barrel and simulated bourrelet sample.Supposing that the axes of both barrel and projectile are parallel,the corresponding contact detection strategies between them are proposed for rifled gun and smooth bore,respectively.Both the hybrid model and several traditional cylindrical models are employed for the contact impact process of the barrel and simulated bourrelt sample,and calculated results are compared with those of finite element simulation.Results show that the hybrid model can capture the trend of physical quantities during the contact impact process for both rifled gun and smooth bore.However,due to its assumptions and the complexity of real contact-impact process between the barrel and bourrelet,the hybrid model can only partially simulate the real contact-impact events.Thus,the following chapters focus on the FEM simulation combined with the parameter identification method.Taking the hybrid analytical contact force model as the prototype,FEM simulation combined with the parameter identification method is used to estimate the unknown contact-impact dynamic parameters,thus obtaining a more suitable model,which can accurately describe the contact-impact process between barrel and bourrelet.(3)In order to test the effectiveness of FEM used for the simulation of complex surface contact-impact process,one verification experiment is carried out.The contact-impact test bench for the barrel sample and simulated bourrelet sample is designed and manufactured.Meanwhile,the FEM model of the bench is established to calculate the simulation results.Comparisons between the experimental results and simulated ones indicate the effectiveness of the FEM during the contact-impact simulating process between complex surfaces,which therefore validates the correctness of simulation results and lay some foundations for the effectiveness of parameter identification results.(4)Taking the 122mm and 155mm caliber howitzers as examples,the FEM elastoplastic dynamic models between barrel and bourrelet during lunching process are built.Consequently,the changes of relevant physical quantities during contact-impact process under different initial indentation velocities can be acquired,including the contact force,indentation,and the corresponding indentation velocity,which provide input data for the parameter identification process.Simulated results show that nearly half of the total number of rifles in the barrel interact with the projectile at the maximum indentation value,indicating that the contact between barrel and bourrelet are not non-conformal.With the increase of the initial indentation velocity,the contact force increases gradually,so does the indentation.Meanwhile,area surrounded by the hysteresis loop is larger,meaning more energy is dissipated.(5)Three parameter identification methods are listed with their advantages and disadvantages,and the estimation process is also introduced.The contact force,indentation and indentation velocity under different initial indentation velocities can be obtained from the FEM analyses.These physical quantities are regarded as the inputs for the parameter estimation process.The mapping relationship between them is clarified.For the 122mm and 155mm caliber howitzers,the genetic algorithm-sequential quadratic programing(GA-SQP)hybrid estimation method is employed to obtain the unknown contact-impact dynamic parameters under each initial indentation velocity,namely contact stiffness parameter,damping factor and exponent.Then,supposing the relationships between dynamic parameters and material properties,geometries and system motion states,the unknown parameters can be obtained.After that,the least square method is employed to fit the relation between the unknown parameters and initial indentation velocities.Finally,the uniform contact force model for 122mm and 155mm caliber howitzers between the barrel and bourrelet can be obtained.(6)The dynamic equations of projectile-barrel coupled system considering the effect of rigid-flexible coupling during the artillery launching process are established.The bearing conditions of the barrel and projectile are analyzed,respectively,among which the uniform contact force model is utilized to describe the contact-impact events between the barrel and bourrelet.Some simulation examples considering different eccentricities of the projectile are conducted.Results show that as the eccentricity of the projectile increases,the amplitude of each variable increases gradually.In addition,due to the gravity of the barrel,vertical motion is severer than the horizontal movement.